Envelope Tracking Systems for Power Amplifiers

2. The envelope tracking system of claim 1 wherein the amplifier input stage is powered by a fixed supply voltage.

3. The envelope tracking system of claim 1 wherein the envelope tracker further includes a control circuit configured to compare the sense current to a plurality of current thresholds of different levels.

4. The envelope tracking system of claim 3 wherein the control circuit includes a hysteretic current comparator.

5. The envelope tracking system of claim 1 wherein the envelope tracker further includes a capacitor connected between an output of the amplifier output stage and the power amplifier supply voltage.

6. The envelope tracking system of claim 5 wherein the envelope tracker further includes a DC-to-DC converter configured to generate a regulated voltage, and an inductor connected between the regulated voltage and the power amplifier supply voltage.

7. The envelope tracking system of claim 5 wherein the amplifier input stage includes a first input configured to receive a reference signal and a second input configured to receive the envelope signal.

8. The envelope tracking system of claim 7 wherein the envelope tracker further includes a current source connected to the second input, and a DC tracking circuit configured to control a current of the current source based on a voltage across the capacitor.

9. The envelope tracking system of claim 7 further comprising a feedback resistor connected between the output of the amplifier output stage and the second input.

11. The mobile device of claim 10 wherein the amplifier input stage is powered by a fixed supply voltage.

12. The mobile device of claim 10 wherein the envelope tracker further includes a control circuit configured to compare the sense current to a plurality of current thresholds of different levels.

13. The mobile device of claim 12 wherein the control circuit includes a hysteretic current comparator.

14. The mobile device of claim 10 wherein the envelope tracker further includes a capacitor connected between an output of the amplifier output stage and the power amplifier supply voltage.

15. The mobile device of claim 14 wherein the envelope tracker further includes a DC-to-DC converter configured to generate a regulated voltage, and an inductor connected between the regulated voltage and the power amplifier supply voltage.

16. The mobile device of claim 14 wherein the amplifier input stage includes a first input configured to receive a reference signal and a second input configured to receive the envelope signal.

17. The mobile device of claim 16 wherein the envelope tracker further includes a current source connected to the second input, and a DC tracking circuit configured to control a current of the current source based on a voltage across the capacitor.

18. The mobile device of claim 16 further comprising a feedback resistor connected between the output of the amplifier output stage and the second input.

20. The method of claim 19 further comprising powering the amplifier input stage using a fixed supply voltage.